<html>
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		.grandparent{
			padding: 40px;
			border: solid 2px #00f;
			width: 400px;
			margin: 20px auto;
			position: relative;
		}
		.parent{
			padding: 10px;
			border: solid 2px #000;
			width: 300px;
			margin: 30px auto;
			position: relative;
		}
		.box{
			border: dashed 1px #f00;
			padding: 20px;
			margin-bottom: 5px
		}
		.box1{
			background-color: #f88;
		}
		.box2{
			background-color: #f00;
		}
		.box3{
			background-color: #0f8;
			position: absolute;
			top: 10px;
			left:10px;
		}
	</style>
</head>
<body>
	<div class="grandparent">
		<div class="parent">
			<div class="box box1">第一个盒子</div>
			<div class="box box2">第二个盒子</div>
			<div class="box box3">第三个盒子</div>
		</div>
	</div>
</body>
</html>